Graphics Reference
In-Depth Information
Feathers are essential not only for flight; they also provide insulation,
helping to keep birds warm or cool, depending on their circumstances.
Because of feathers' thermal properties, penguins are able to withstand all
that the Antarctic winter can throw at them, surviving months of extremely
low temperatures. At the other end of the scale, ostriches are able to keep
cool under extreme high temperatures due to the nature of their feathers.
Although they have become completely useless for flight, the filaments
having lost their barbs, making ostrich feathers incapable of being zipped
together and forming an interlocking, smooth, seamless edge for an
aerodynamic wing, they offer protection both from the midday heat and from
the cold at night.
Feathers also play an important role in providing plumage designed to both
hide and attract. Feathers have become an essential aspect of camouflage,
particularly for the vulnerable nesting female, and they have become an
essential part of the male's display when trying to attract a mate. There are
some feathers that have become so modified and specialized that they
actually
impede
flight. It could be argued that the beautiful display feathers
of some birds, rather than contributing to their success as a species, have in
part endangered their very existence by drawing attention not only from
prospective mates but also from prospective predators. Man has hunted
some birds to near extinction for the aesthetic qualities of their plumage.
Despite these examples, feathers are an important part of a bird's survival
strategy.
Wings
If one feature distinguishes birds from any other animal, it must be the feather.
The second and perhaps more obvious feature is the wing. The majority of
birds share both of these features: They all have feathers and most have wings,
or at least vestiges of wings.
A bird's wing has three distinct bands of feathers covering it. The largest
flight feathers, located on the outer edge of the wing, can be broken into
primary, secondary, and tertiary feathers. The primary feathers are the longest
and deliver the maximum power to propel the bird forward. The secondary
feathers, located on the forearm, create a large surface area, providing lift. The
tertiary feathers are attached to the upper arm and ensure a seamless surface
between the body and the outer wing. These feathers are covered by two
other rows of feathers, called
coverts
. These are aligned in such a manner that
enables them to slide over one another during flight and thereby maintain
the aerodynamic shape necessary to reduce drag and turbulence and for
continued stability in the air. The
alua
, a group of feathers attached to the
bird's thumb, is normally held flat against the bird's wing. During slow-speed
flying, the alua is extended to redirect and increase air flow over the wing, to
prevent stalling.
